The primary goals of this project are to develop analytical methods for the differentiation of subgroup fertility dynamics and the time contingent correlates of fertility, then to apply them to the accumulated data of the American fertility surveys in view of examining subgroup variations and changes in the sequential process of family building during 1940-70. It is proposed that such an analysis of the socio-cultural fertility dynamics of subgroups and the sequential correlates would help our understanding of the changing social institution of the American family during these most recent decades. For measurement of temporal patterns of fertility we have found that a simple data transformation is sufficient for normalization of closed birth intervals of the controlled fertility of the U. S. This has led us to a simplification in analyzing subgroup differences in timing patterns of birth, as well as to believe that regularity in measured birth interval data may not suffice the required estimate of parameters of an overly elaborate birth process model. Other time-contingent correlates of fertility are being explored for suitable data transformations which will facilitate model conceptualization as well as analysis of group differences. Subgroup attributes are also being investigated via discrete multivariate analysis. Having identified both sequential and time-invariable correlates of fertility, which is inherently a temporal process, we will be reporting the variations and changes in subgroup processes of family formation in 1940-70 for the U. S.